United Nations, May 2 (Reuters): UN secretary-general Kofi Annan challenged world leaders today to breathe life into a key nuclear disarmament treaty, with new countries acquiring dangerous weapons and nuclear powers slow to disarm.

Annan opened a monthlong conference on the 1970 Nuclear Non-proliferation Treaty that appeared deadlocked before it began, with the US wanting the focus on Iran and North Korea's nuclear programmes.

The 188 members of the treaty, the cornerstone in arms reduction treaties, meet every five years to review progress and set new goals. Only the US, Russia, Britain, France and China are permitted to have nuclear arms while all other countries vow to give up atomic warheads for good.

But most nations complain that the nuclear powers, mainly the US and Russia, have moved far too slowly in abiding by the NPT, which calls for them to move toward dismantling their arsenals.

Iran threatened today to resume producing nuclear fuel. And North Korea, which said it has nuclear weapons and withdrew from the NPT, on the eve of the conference apparently launched a short-range missile into the Sea of Japan, adding to tensions.

In his remarks, Annan resurrected the threat of a nuclear catastrophe: 'Imagine, just for a minutes what the consequences would be. Tens, if not hundreds, of thousands of people would perish in an instant.'

The secretary-general said withdrawal from the treaty by any country needed to be addressed or 'the most basic collective reassurance on which the treaty rests will be called into serious question.'

On the Iranian problem, he said that 'states that wish to exercise their undoubted right to develop and use nuclear energy for peaceful purposes must not insist that they can only do so by developing capacities that might be used to create nuclear weapons.'

Despite resolutions and treaties, Annan said the world could not afford to be complacent. 'The plain fact is that the regime has not kept pace with the march of technology and globalisation, and developments of many kinds in recent years have place it under great stress,' he said.

A host of foreign ministers have arrived for the conference, which ends on May 27, including Iran's Kamal Kharrazi, who has scheduled private meetings with Mohamed ElBaradei, head of the International Atomic Energy Agency.

But North Korea won't attend. India and Pakistan, which have nuclear weapons, and Israel, assumed to also have atomic arms, have not signed the treaty. The Bush administration, which has also scorned a nuclear test-ban treaty, is sending a mid-level delegation.